The present invention relates to the field of shaped charge firing guns for perforating casing and the borehole rock surface in hydrocarbon producing wells. More particularly, the present invention relates to a high density well perforating apparatus.
Well casing is typically installed in a borehole drilled into subsurface geologic formations. The well casing prevents uncontrolled migration of subsurface fluids between different well zones, and provides a conduit for installing production tubing in the well. The well casing also facilitates the running and installation of production tools in the well.
To produce hydrocarbon fluids from a subsurface geologic formation, the well casing is perforated by high velocity jets from perforating gun shaped charges. A firing head in the perforating gun is actuated to detonate a primary explosive and to ignite a booster charge connected to a primer or detonating cord. The detonating cord transmits a detonation wave to each shaped charge. Booster charges within each shaped charge activate explosive material to collapse a shaped charge liner into a shaped charge cavity. The collapsing liner generates a high velocity jet for penetrating the well casing and the adjacent geologic formation. These jets perforate the well casing and establish a flow path for reservoir fluids from the subsurface geologic formations to a well casing interior. In a well having multiple production zones, packers isolate selected zones of the well casing, and production tubing transports the reservoir fluids from each zone to the well surface.
Multiple casing perforations are desirable in certain hydrocarbon producing zones. To form multiple perforations, shaped charges are installed in the perimeter of a perforating gun housing. The individual shaped charges are mechanically positioned in spirals and in other geometric orientations within the perforating gun. These shaped charge geometric orientations create "dead spaces" between adjacent shaped charges which limits the perforation density of the charges and reduces the perforating capability of the gun.
Perforating gun systems typically attach individual shaped charges to a charge carrier. This process requires significant labor and does not easily permit a high concentration of shaped charges in a perforating gun system. To reduce the cost of shaped charge guns, carrier strips sometimes connect shaped charges in a perforating system. However, such charge carrier strips often fragment upon detonation and undesirably increase the debris within the wellbore.
Known perforating guns are expensive and limit the number of shaped charges that can be positioned within a selected wellbore segment. A need therefore exists for an improved perforating gun system that reduces manufacturing cost and that provides a high density shot pattern.